The field of the present disclosure is systems and methods for magnetic resonance imaging (“MRI”). More particularly, the present disclosure relates to systems and methods for calibrating magnetic resonance images to produce high-resolution maps of relaxation parameters, such as longitudinal or transverse relaxation times.
Cardiovascular disease is the leading global cause of death, accounting for 17.3 million deaths per year. Fibrosis is an important marker in many types of heart disease, including ischemic heart disease, atrial fibrillation, cardiac amyloidosis, cardiomyopathy, myocarditis, and aortic stenosis. Therefore, the ability to characterize and quantify the three-dimensional architecture of fibrosis in the heart is of much clinical interest.
The ability to characterize the three-dimensional architecture of the scar tissue area is of much interest in the field of cardiology. Current methods in the field to detect scar tissue and delineate areas of tissues with different characteristics are laborious and have several limitations. Myocardial viability based on electrical voltage of the tissue is highly dependent on catheter orientation and contact to tissue. Furthermore, the ability to properly identify tissue types outside of dense scar are even more difficult because thresholds for voltage collected by catheters used for scar analysis are variant between patients. Electrical pacing from catheters in-vivo has been shown to better delineate scar tissue, but this is a time intensive process.
MRI provides the ability to differentiate tissue based on innate tissue characteristics. In particular, parametric mapping, T1-weighted imaging, and T2-weighted imaging have been able to identify changes in tissue stages as a result of acute or chronic inflammatory responses. Transverse relaxation time (“T2”) has been mentioned for more acute responses to identify edema; however, the longitudinal relaxation time (“T1”) characteristic of tissue has been used for identifying infarct using methods such as delayed enhancement and the modified look-locker inversion recovery (“MOLLI”) technique.
Delayed enhancement, also referred to as late gadolinium enhancement (“LGE”), provides a large signal where dense scar tissue has formed based upon a user specified inversion time, at which normal myocardial tissue signal is nulled. This technique provides information of scar tissue in relative signal intensity, which can be difficult to standardize on an individual patient basis because imaging time post contrast and heart rate are uncontrollable variables.
MOLLI imaging directly provides T1 magnetization recovery values for each pixel of the image, with an acquisition time of approximately 10-15 seconds for a 1.3×1.3×8.0 mm resolution image. Due to the sampling needed at specific time points to acquire this data (in addition to the regular difficulties of cardiac imaging such as patient motion, breathing, magnetic field inhomogeneity), this can make it difficult to use the MOLLI sequence for evaluation of T1 tissue evaluation. The acquisition of multiple sample points along the T1 recovery curve makes it difficult to achieve sub-millimeter or close to sub-millimeter isotropic resolution.
Thus, there remains a need for a robust method that can provide high resolution T1 images for use in fully understanding the complexity of fibrotic tissue in patients with ischemic and non-ischemic cardiomyopathies.